The refractive indices of some liquid and gas were measured by using one and two-side leaky mode method. Liquid or gas wag driped or filled between prism and substrate, so that these three layers media formed one or two sides leaky weveguide. The mode refractive indices of resonant modes were measured by using the prism coupler, and the refractive index of the liquid or gas was determined from corresponding mode equations. Measure(?) results shown that errors of the refractive indices are with in 1~3×10-4. The measnremenli accuracies were analysed and discussed theoretically.